The present invention relates to an acrylic monomer composition and an acrylic copolymer that serve suitably as materials for highly transparent and mouldable heat resistant resins, and a heat resistant resin using such an acrylic copolymer.
Methacrylic resins have found widespread applications for optics associated use in automobiles, home electric appliances, and the like, since they are highly colourless and transparent, glossy on surface, and durable in tough climates, as well as well-balanced in mechanical properties, thermal properties, surface hardness, and mouldability.
Recently, in these applications, the light sources are very often configured in a close proximity of the resin for better flexibility in design, smaller size, and higher performance. Hence, heat resistant resins that boast even better thermoresistance are earnestly desired.
A well-known method of preparing a heat resistant resin involves, for example, a technique to improve thermoresistance by crosslinking a copolymer of methyl methacrylate (MMA) and a multifunctional methacrylate such as neopenthyl glycol dimethacrylate. However, the resin prepared by that method boasts better a thermoresistance but has a low polymer fluidity when heated and poor mouldability.
Other well-known methods involves a technique to improve thermoresistance by side chains that are introduced by copolymerising MMA with an xcex1-methyl styrene or with a maleic anhydride or with an ester methacrylate having a bulky alkyl group such as bornyl methacrylate. The method, although effectively improving thermoresistance by the introduction of bulky side chains, entails poor mechanical strength of the resin.
Further well-known methods involves a technique to improve thermoresistance by improving rigidness of the principal chain by a cyclic structure introduced to a principal chain by copolymerising MMA with a cyclic monomer such as an N-substituted maleimide and a maleic anhydride. The technique to introduce a cyclic structure to a principal chain have advantages, in comparison with the technique to introduce bulky side chains, that thermoresistance is greatly improved for a relatively small drop in mechanical strength. However, cyclic monomers are generally not well copolymerised with MMA, limited in capability to have thermoresistance imparting constituent introduced, and are likely to remain as an unreacted monomer when the polymerisation is completed. The unreacted residue in a polymer formed of cyclic monomers causes colouring and degradation in weatherability and other properties when the polymer is moulded into a moulded product.
Accordingly, a U.S. Pat. No. 2,146,209 discloses, as a technique to introduce a cyclic structure to a principal chain, a technique to introduce a six-memberedring imide structure (glutaric imide cyclic structure) to a principal chain by reacting polymethyl methacrylate (PMMA) with a primary alkyl amine. Further, Japanese Laid-Open Patent Application No. 60-20905/1985 (Tokukaisho 60-20905, published on Feb. 2, 1985) discloses a technique to introduce a glutaric anhydride structure to a principal chain by subjecting a copolymer of MMA with either a methacrylic acid or a methacrylic acid t-butyl ester to a heating treatment. The introduction of a six-membered cyclic structure to a principal chain by means of the aforementioned side chain reaction improves thermoresistance, as well as imparts a better performance in mechanical strength than methacrylic resins. However, the introduction of a six-membered ring imide structure causes colouring due to a nitrogen atom in unreacted free amine and the like when a copolymer having the structure is moulded. Further, the copolymer formed by introducing a glutaric anhydride structure is highly reactable with water, alcohol, and amine, the cycle thereof is easy to break, and therefore thermoresistance is not effectively improved.
Accordingly, as a method of preparing a heat resistant resin that is free from the preceding problems, Polym. Prepr., 8,11,576(1967), J. Polym. Sci., A., 27,751(1989) discloses a method of obtaining a heat resistant resin by subjecting a copolymer of styrene and a 2-(hydroxymethyl) acrylate alkyl ester to a heating treatment and thus lactone cyclising the copolymer. However, the method described in the document has a problem that part of the polymer is crosslinked and cannot be moulded by melting to prepare a heat resistant resin.
Accordingly, Japanese Laid-Open Patent Application No. 9-241323/1997 (Tokukaihei 9-241323, published on Sep. 16, 1997) discloses a technique to prevent polymer crosslinking in the heating treatment and resultant lactone cyclisation of a copolymer that has a structural unit derived from 2-(hydroxymethyl)acrylate alkyl ester, by subjecting the copolymer to a heating treatment in the presence of an esterificating catalyst or of a solvent.
However, the technique is still not able to prevent crosslinking to satisfactory levels. The heat resistant resin obtained by the method has problems when applied in a field where a higher degree of transparency and mouldability is required. Moreover, in manufacture of a heat resistant resin by subjecting a copolymer having a structural unit derived from 2-(hydroxymethyl) acrylate alkyl ester to a heating treatment, gelation becomes apparent only after the obtained polymer is actually subjected to a heating treatment to manufacture a heat resistant resin, and therefore if gelation should occur, significant amounts of time, cost, and labour are wasted in the removal of resultant gel products and cleaning of apparatus.
In light of the above problems, the present invention has an object to offer a highly transparent and mouldable, gelation-free heat resistant resin, as well as an acrylic monomer composition and an acrylic copolymer that can be used suitably as materials to manufacture the heat resistant resin.
In order to achieve the above object, the inventors of the present invention have diligently worked and found that an acrylic copolymer formed by copolymerising an acrylic monomer having a specific structure with another monomer that is copolymerisable with the acrylic monomer, either the acrylic copolymer having a specified acid value or the viscosity of a tetrahydrofuran solution dissolving the acrylic copolymer under a specified condition having a specified viscosity, is suitable as a material to manufacture a highly transparent and mouldable heat resistant resin that does not gel when manufactured, and also found that the acrylic copolymer having the specified acid value can be readily prepared by regulating the acid value of the monomer composition that contains the acrylic monomer having a specific structure and another monomer that is copolymerisable with the acrylic monomer, which led to the completion of the present invention.
Specifically, the acrylic monomer composition in accordance with the present invention, in order to solve the aforementioned problems, is an acrylic monomer composition containing an acrylic monomer represented by general formula (1) 
where each of R1 and R2 is either a hydrogen atom or an organic residue, and another monomer that is copolymerisable with the acrylic monomer, and is characterised in that it has an acid value of 5 mgKOH/g or less.
Further, the acrylic copolymer in accordance with the present invention, in order to solve the aforementioned problems, is an acrylic copolymer formed by copolymerising an acrylic monomer represented by general formula (1) with another monomer that is copolymerisable with the acrylic monomer, and is characterised in that it has an acid value of 5 mgKOH/g or less.
Moreover, the acrylic copolymer in accordance with the present invention, in order to solve the aforementioned problems, is an acrylic copolymer formed by copolymerising an acrylic monomer represented by general formula (1) with another monomer that is copolymerisable with the acrylic monomer, and is characterised in that the 1% tetrahydrofuran solution formed by subjecting the acrylic copolymer to a heating treatment at a temperature of 250xc2x0 C. for 30 minutes and thereafter dissolving the acrylic copolymer in tetrahydrofuran has a viscosity ranging from 10 cps to 10,000 cps at 25xc2x0 C.
The heat resistant resin in accordance with the present invention, in order to solve the aforementioned problems, is characterised in that it is formed by heating the acrylic copolymer.
Further, the method of preparing the acrylic copolymer in accordance with the present invention, in order to solve the aforementioned problems, is characterised in that the acrylic monomer composition is polymerised.
According to the present invention, a highly transparent and mouldable heat resistant resin that does not gel when manufactured can be offered by using, as a material for heat resistant resin, an acrylic copolymer formed by copolymerising an acrylic monomer represented by general formula (1) with another monomer that is copolymerisable with the acrylic monomer, the 1% tetrahydrofuran solution formed by subjecting the acrylic copolymer to a heating treatment at a temperature of 250xc2x0 C. for 30 minutes and thereafter dissolving the acrylic copolymer in tetrahydrofuran having a viscosity ranging from 10 cps to 10,000 cps at 25xc2x0 C. The a heat resistant resin is readily obtained by heating the acrylic copolymer.
Especially, an acrylic copolymer formed by copolymerising an acrylic monomer represented by general formula (1) with another monomer that is copolymerisable with the acrylic monomer, and having an acid value of 5 mgKOH/g or less meets the above regulation on viscosity at a temperature of 25xc2x0 C., if being subjected to a heating treatment at a temperature of 250xc2x0 C. for 30 minutes and thereafter dissolved in tetrahydrofuran to produce a 1% tetrahydrofuran solution. Besides, from that acrylic copolymer is obtainable a highly transparent and mouldable heat resistant resin that does not gel when manufactured and that can be moulded by melting. Further, if the acrylic copolymer is used, a heat resistant resin is obtainable which readily lactone cyclises and boasts excellent thermoresistance among various properties.
Further, if an acrylic monomer composition is used, the acrylic monomer composition containing an acrylic monomer represented by general formula (1) and another monomer that is copolymerisable with the acrylic monomer, and having an acid value of 5 mgKOH/g or less, the aforementioned acrylic polymer having an acid value of 5 mgKOH/g or less is readily obtained.
Therefore, if the aforementioned acrylic monomer composition is used, the acrylic polymer having an acid value of 5 mgKOH/g or less and the acrylic polymer of which the 1% THF solution has a viscosity of 10 cps to 10,000 cps at a temperature of 25 xc2x0 C. can be readily obtained.
The following description will discuss further details in accordance wit the present invention.
The acrylic copolymer in accordance with the present invention is a copolymer formed by polymerising an acrylic monomer composition containing an acrylic monomer represented by general formula (1) and another monomer that is copolymerisable with the acrylic monomer, and has an acid value of 5 mgKOH/g or less.
The acrylic monomer represented by general formula (1), used as a material in the method of preparing the acrylic copolymer, although not being limited in any special manner, is preferably a hydroxyl group containing monomer such that in the formula each of the substitution groups represented by R1 and R2 is either a hydrogen atom or an organic residue.
Specific examples of the organic residue that in some cases makes up the substitution groups represented by R1 and R2 include a linear or branched alkyl group having one to 18, preferably one to 12, carbons, such as a methyl group, an ethyl group, an N-propyl group, an iso-propyl group, an N-butyl group, a sec-butyl group, an N-hexyl group, a cyclohexyl group, an N-octyl group; a 2-ethylhexyl group, or a lauryl group; a non-substituted or substituted aryl group, having preferably six to 12 carbons, such as a phenyl group, a toluic group, a xylyl group, a naphthalene group, and a benzyl group; a hydroxy alkyl group having one to six carbons, such as a hydroxy methyl group, a 2-hydroxy ethyl group, a 2-hydroxy propyl group, a 3-hydroxy propyl group, a 4-hydroxy butyl group, and a 6-hydroxy hexyl group; and a heterocyclic group. Note that the substitution group represented R1 is a substitution group derived from an aldehydric compound.
Specific examples of the acrylic monomer represented by general formula (1) include methyl-2-(hydroxymethyl) acrylate, ethyl-2-(hydroxymethyl) acrylate, isopropyl-2-(hydroxymethyl) acrylate, N-butyl-2-(hydroxymethyl) acrylate, and t-butyl-2-(hydroxymethyl) acrylate.
Any one of these acrylic monomers may be used alone, or alternatively, a plurality of them may be used in combination. Among the acrylic monomers mentioned above, methyl-2- (hydroxymethyl) acrylate and ethyl-2-(hydroxymethyl) acrylate are especially preferred since a desired acrylic copolymer is readily obtainable from them.
The above acrylic monomers used in accordance with the present invention are readily obtainable by a well-known method: for example, a method of carbonylation and subsequent esterification of propargyl alcohol (U.S. Pat. No. 3,066,165), a method of reaction (Wittig-Horner Reaction) of trialkyl phosphonoacetate with formalin in the presence of potassium hydroxide (Org. Synth., 66,220 (1988)) a method of reacting associated vinyl with aldehydric compounds in the presence of a tertiary amine compound as a catalyst and in the presence of water (Japanese Laid-Open Patent Application No.7-285906/1995 (Tokukaihei 7-285906, published on Oct. 31, 1995; Corresponding U.S. Pat. No. 5,703,270)), or a method of subjecting an acrylic monomer obtained with one of these methods to a cleaning treatment with a basic substance. Note that the cleaning treatment will be detailed later.
The monomer that is copolymerisable with the acrylic monomer represented by general formula (1) (hereinafter, in some cases will be referred to as a copolymerisation constituent), although not being limited in any special manner, is suitably a vinyl monomer represented by general formula (2) due to good reaction and polymerisation properties with the acrylic monomer represented by general formula (1) and ready obtainability of a desired heat resistant resin: 
where R3 is either a hydrogen atom or a methyl group, R4 is a hydrogen atom, an alkyl group having one to six carbons, a phenyl group, an xe2x80x94OCOCH3 group, a xe2x80x94CN group, a xe2x80x94COR5 group, or a xe2x80x94COOR6 group, and each of R5 and R6 is either a hydrogen atom or an organic residue.
The vinyl monomer represented by general formula (2), although not being limited in any special manner, is a vinyl monomer where the substitution group R3 is either a hydrogen atom or a methyl group, the substitution group R4 is a hydrogen atom, an alkyl group having one to six carbons, a phenyl group, an xe2x80x94OCOCH3 group, a xe2x80x94CN group, a xe2x80x94COR5 group, or a xe2x80x94COOR6 group, and each of R5 and R6 is either a hydrogen atom or an organic residue. The organic residue, as the substitution groups R5 and R6, is specifically an alkyl group having one to 18, an aryl group, a hydroxy alkyl group having one to six carbons having one to six carbons, or a heterocyclic group.
Examples of the vinyl monomer represented by general formula (2) include methyl (meth)acrylate, ethyl (meth)acrylate, cyclo hexyl (meth)acrylate, styrene, xcex1-methyl styrene, acrylonitrile, methyl vinyl ketone, ethylene, propylene, vinyl acetate.
Further, apart from the vinyl monomer represented by general formula (2), specific examples of the copolymerisation constituent, although not being limited in any special manner, include halogenated vinyls, such as vinyl chloride, and chloride vinylidene; maleimides, such as maleimide, N-phenyl maleimide, N-cyclohexyl maleimide, N-benzyl maleimide, N-isopropyl maleimide, N-(2-chlorophenyl) maleimide, and N-(2-bromophenyl) maleimide; a maleic anhydride; maleates, such as maleic acid dicyclohexyl; fumarates, such as fumaric acid dibutyl and fumaric acid dicyclohexyl; xcex1-methylene-xcex3-butyrolactone.
Any one of these copolymerisation constituents may be used alone, or alternatively, a plurality of them may be used in combination. Among the monomers mentioned above, methyl methacrylate, methacrylic acid cyclohexyl, and styrene are especially suitably used.
The acrylic copolymer in accordance with the present invention can be readily manufactured by copolymerising the acrylic monomer represented by general formula (1) with the monomer (a copolymerisation constituent) that is copolymerisable with the acrylic monomer.
The acid value of the acrylic copolymer is adjustable by adding a basic compound that does not cause colouring and other problems in manufacture of a heat resistant resin: for example, sodium carbonate, sodium hydrogencarbonate, sodium acetate, potassium acetate, sodium acrylate, sodium methacrylate. An acid value of 5 mgKOH/g or less can be imparted to the acrylic copolymer by causing a polymerisation reaction of an acrylic monomer composition having an acid value of 5 mgKOH/g or less that contains the acrylic monomer represented by general formula (1) and the monomer that is copolymerisable with that acrylic monomer (copolymerisation constituent), preferably the vinyl monomer represented by general formula (2).
If the acrylic copolymer has an acid value of 5 mgKOH/g or less, the resultant heat resistant resin readily lactone cyclises, boasts excellent thermoresistance, transparency and mouldability, does not gel when manufactured, and can be moulded by melting. By contrast, if the acrylic copolymer has an acid value exceeding 5 mgKOH/g, the resultant heat resistant resin gels when manufactured and has problems in transparency, mouldability, etc.
The acrylic monomer represented by general formula (1) and the monomer that is copolymerisable with that acrylic monomer (copolymerisation constituent) are mixed to form the acrylic monomer composition, at a mixture ratio appropriately specified depending on properties desirably imparted to the heat resistant resin, the constituents of the acrylic monomer composition to be used, and the like.
For example, the mixture ratio of the acrylic monomer represented by general formula (1) and its copolymerisation constituent in the acrylic monomer composition, i.e., the ratio of the acrylic monomer represented by general formula (1) to the copolymerisation constituent, is preferably in a rage from 1:9 to 7:3.
If the mixture ratio of the acrylic monomer represented by general formula (1) in the acrylic monomer composition is lower than the preceding mixture ratio, the resultant heat resistant resin possibly does not have excellent thermoresistance. By contrast, if the mixture ratio of the acrylic monomer represented by general formula (1) in the acrylic monomer composition is higher than the mixture ratio, the resultant heat resistant resin has improved thermoresistance, but the improvement in thermoresistance is not so effective to match the increase in the mixture ratio, which is not economically favourable.
Further, if the acrylic monomer composition does not contain a copolymerisation constituent, i.e., if the acrylic polymer obtained is a homopolymer of the acrylic monomer represented by general formula (1), the resultant acrylic polymer gels when manufactured even with an acid value being 5 mgKOH/g or less, and the obtained heat resistant resin undesirably lacks excellent transparency and mouldability.
In summary, the acrylic copolymer in accordance with the present invention is readily obtained by preparing the acrylic monomer composition containing an acrylic monomer represented by general formula (1) and another monomer that is copolymerisable with the acrylic monomer (copolymerisation constituent) so that the acrylic monomer composition obtained has an acid value of 5 mgKOH/g or less, and thereafter causing a polymerisation reaction of the acrylic monomer composition.
The method of preparing the acrylic monomer composition is not limited in any special manner. Examples of such a method include a method of subjecting a monomer composition containing an acrylic monomer and another monomer that is copolymerisable with the acrylic monomer with a basic substance to a cleaning treatment, the acrylic monomer being the acrylic monomer represented by general formula (1) or a monomer that, if subjected to a cleaning treatment with a basic substance, produces the acrylic monomer represented by general formula (1), specifically an acrylic monomer that is obtainable by either of the manufacturing methods disclosed or described in U.S. Pat. No. 3,066,165, Org. Synth.,66,220(1988), and Japanese Laid-Open Patent Application No. 7-285906 (Tokukaihei 7-285906); and a method of adjusting the acid value of the individual monomer constituent constituting the acrylic monomer composition to 5 mgKOH/g or less in advance by a cleaning treatment with a basic substance.
The basic substance used in the cleaning treatment is not limited in any special manner: specific examples include a basic ion-exchange resin, sodium hydrogencarbonate, and sodium hydroxide. Specific examples of the basic ion-exchange resin include basic ion-exchange resins available from Rohm and Haas Co., such as Amberlight A-21, Amberlight IRA-68, Amberlight IRA-60E, Amberlight IRA-35, and Amberlight IRA-45; basic ion-exchange resins available from Mitsubishi Chemical Industries Ltd., such as Diaion WA-10, Diaion WA-20, and Diaion WA-30; basic ion-exchange resins available from Dow Chemicals Co., such as Dowex WGR2, and Dowex 66; and basic ion-exchange resins available from Sumitomo Chemical Co., Ltd., such as Duolite A-368, and Duolite A-568, Duolite A-578. Among these basic substances, basic ion-exchange resins are suitable for use.
An example of the cleaning treatment method is to stir the material subjected to a cleaning treatment together with a basic substance in the presence of water and/or an organic solvent as required, and thereafter fractionate the obtained product. The material having been subjected to a cleaning treatment may be directly used as a material for an acrylic copolymer, but is preferably further distilled after the cleaning treatment for some usages.
The polymerisation reaction of the acrylic monomer composition, i.e., the copolymerisation reaction of the acrylic monomer represented by general formula (1) with the monomer that is copolymerisable with the acrylic monomer can be readily caused by radical polymerisation reaction, ionic polymerisation reaction, and the like. However, preferably, radical polymerisation reaction is employed. Further, for the radical polymerisation reaction, various prior art methods may be employed: for example, a bulk polymerisation technique, a solution polymerisation technique, and a suspension polymerisation technique. A solution polymerisation technique is especially suitable for use due to easy control of polymerisation reaction.
The radical polymerisation initiator used for the radical polymerisation reaction is not limited in any special manner: examples include azo polymerisation initiators, such as azobis isobutyronitrile, and peroxide polymerisation initiator, such as a benzoyl peroxide.
Further, the quantity of the polymerisation initiator used, polymerisation time, polymerisation temperature, and other reaction conditions are not limited in any special manner, but appropriately specified according to the polymerisation initiator used, constituents of the acrylic monomer composition, and polymerisation system. Note that the polymerisation reaction is preferably caused under a nitrogen or other inert gas atmosphere
The acrylic copolymer obtained preferably has a degree of polymerisation such that the weight-average molecular weight is in a range from 5,000 to 1,000,000, and preferably from 10,000 to 500,000. If the weight-average molecular weight is less than 5,000, it is difficult to maintain mechanical properties over a long period of time, and poses problems for long term uses. Further, if the weight-average molecular weight exceeds 1,000,000, the improvement in performance is not so effective to match the labour, manufacturing costs, manufacture conditions, etc. required to obtain an acrylic copolymer that exceeds 1,000,000 in weight-average molecular weight, which is not economically favourable.
Further, in the polymerisation reaction, in order to adjust the weight-average molecular weight, a chain transfer agent, such as methyl mercapt propionic acid or dodecyl mercaptan, may be added as required.
The acrylic copolymer in accordance with the present invention is obtainable by, for example, adding a radical polymerisation initiator at a ratio of 0.1 percent by weight to 5 percent by weight to the quantity of the acrylic monomer composition, i.e., the total amount of the acrylic monomer represented by general formula (1) and the monomer that is copolymerisable with the acrylic monomer in the presence of an organic solvent that is inert to the polymerisation reaction, causing a polymerisation reaction at a polymerisation temperature of 60xc2x0 C. to 150xc2x0 C. for one to 10 hours, removing the organic solvent used for the polymerisation reaction, and letting the obtained copolymer settle in a poor solvent to remove residual monomer.
The acrylic monomer composition in accordance with the present invention, if used as a material, can normally produce an acrylic copolymer having an acid value 5 mgKOH/g or less from the polymerisation reaction. The aforementioned basic compound that does not cause colouring and other problems in manufacture of a heat resistant resin may be added so as to adjust the acid value of the acrylic copolymer.
The heat resistant resin in accordance with the present invention is readily obtainable by heating the acrylic copolymer and removing volatile constituent. In the present invention, a heat resistant resin refers to a resin, with improved thermoresistance in comparison to a base resin, obtained by copolymerising the aforementioned copolymerisation constituent (another monomer) with a specific monomer constituent and, if necessary, introducing a specific structure or function group (consequently to the base resin), where the base resin is defined as a resin formed from the polymerisation of the aforementioned copolymerisation constituent (another monomer). The heat resistant resin in accordance with the present invention, if an acrylic copolymer with a regulated acid value is used as the material therefor, does not gel, boasts excellent transparency and mouldability, and is capable of being moulded by melting.
However, typically, gelation becomes apparent only after a polymer as a material to produce a heat resistant resin is subjected to a heating treatment to manufacture the heat resistant resin, and therefore if gelation should occur, significant amounts of time, cost and labour are wasted in the removal of resultant gel products and cleaning of apparatus.
For these reasons, the ability to know possibilities of gelation occurring for certain is very important in industrial use. Therefore, by confirming the possibility in advance before manufacture of a heat resistant resin, the resultant heat resistant resin does not gel during manufacture, and is readily given highly transparent, mouldable features.
Accordingly, the inventors of the present invention have diligently worked on conditions under which the heat resistant resin does not gel when manufactured, and found that if an acrylic copolymer is formed by copolymerising an acrylic monomer represented by general formula (1) with another monomer that is copolymerisable with the acrylic monomer, or preferably with a vinyl monomer represented by general formula (2), subjected to a heating treatment for 30 minutes at a temperature of 250xc2x0 C., and dissolved in THF to produce a 1% THF solution having a viscosity ranging from 10 cps to 10,000 cps at 25xc2x0 C., the resultant heat resistant resin does not gel during manufacture, and is given highly transparent, mouldable features.
The inventors of the present invention have further found that the acrylic copolymer formed by copolymerising an acrylic monomer represented by general formula (1) with another monomer that is copolymerisable with the acrylic monomer, and having an acid value of 5 mgKOH/g or less satisfies those conditions.
Accordingly, with those findings in mind, it could be understood that if a gelation test is conducted as a preparatory test before the manufacture of a heat resistant resin, so as to estimate gelation by measuring the viscosity of a 1% THF solution formed by dissolving the resultant acrylic copolymer at 25xc2x0 C., and according to test results only the acrylic copolymer of which the 1% THF solution has a viscosity ranging from 10 cps to 10,000 cps at a temperature of 25xc2x0 C. is selectively used as a material for heat resistant resin, it is possible to prevent production of gel products in the manufacture of a heat resistant resin, and to stably obtain a highly transparent, mouldable heat resistant resin. Further, by conducting the gelation test as a preparatory test before the manufacture of a heat resistant resin, it can be quickly estimated whether or not gelation occurs during the manufacture of a heat resistant resin.
The gelation test is, specifically, conducted by the following scheme. First, 10 g of an acrylic copolymer obtained is taken on an aluminum plate, placed in a thermostatic tank that is set to a temperature of 250xc2x0 C. in advance, and subjected to a heating treatment for 30 minutes. Next, 1 g of the acrylic copolymer treated with heat is taken and dissolved in 99 g of THF to prepare a 1% THF solution, and 1 cc of the 1% THF solution is measured for viscosity at a temperature of 25xc2x0 C. using an E-type viscosity meter (a VICONIED type available from Tokyo Keiki Co. Ltd.) with the rotor set to 0.8xc2x0.
Further, since the acrylic monomer represented by general formula (1) is an acrylic monomer having reactive hydroxyl groups, if the ratio of the acrylic monomer is too high in polymerisation reaction, gelation becomes likely to occur from partial crosslinking in the manufacture of a heat resistant resin. Therefore, if the acid value is not adjust to the specified range, precise control of polymerise conditions is essential, resulting in a more complex operation. Accordingly, by conducting a gelation test and obtaining such polymerisation reaction conditions that the viscosity of a 1% THF solution at a temperature of 25xc2x0 C. satisfies the regulations in the gelation test, the resultant acrylic copolymer becomes suitable as a material for a heat resistant resin that does not gel during manufacture, and that has high transparency and mouldability. In other words, in order to obtain an acrylic copolymer suitable as a material for a heat resistant resin that has excellent transparency and mouldability, an acrylic monomer represented by general formula (1) and another monomer that is copolymerisable with the acrylic monomer should be copolymerised under such polymerisation reaction conditions that the viscosity of a 1% THF solution at a temperature of 25xc2x0 C. satisfies the regulations in the gelation test.
The heating device used in the heating treatment of the acrylic polymer in accordance with the present invention to manufacture the heat resistant resin is not limited in any special manner as long as the heating device is capable of heating the acrylic polymer and removing the volatile constituent thereof. However, the heating device is preferably a heating furnace, a pushing device, or the like that has, for example, a vacuum creating function to remove the volatile constituents.
The heating temperature of the heating treatment, although not being limited in any special manner, is preferably in a range from 150xc2x0 C. to 350xc2x0 C., and more preferably from 200xc2x0 C. to 350xc2x0 C.
The heating time of the heating treatment is specified as required by the degree of thermoresistance and the like, and not limited in any special manner. However, the heating time typically is in a range from one to five hours.
Further, in the heating treatment, protonic acids, such as acetate, oxalic acid, and maleic acid; phosphonium salts, such as bromotetramethyl phosphonium, bromotetraethyl phosphonium, bromotetrabutyl phosphonium, and bromotetrabutyl triphenyl phosphonium. By adding these compounds, the heat resistant resin can be effectively manufacture as desired even at low heating temperatures.
As detailed above, the acrylic polymer in accordance with the present invention is a copolymer formed by copolymerising an acrylic monomer represented by general formula (1) with another monomer that is copolymerisable with the acrylic monomer, or preferably with a vinyl monomer represented by general formula (2), and can be used suitably as a material for a highly transparent and mouldable heat resistant resin that does not gel when manufactured if regulations are met in the gelation test that the viscosity of a 1% THF solution at a temperature of 25xc2x0 C. is in a range from 10 cps to 10,000 cps.
Further, the acrylic polymer formed by copolymerising an acrylic monomer represented by general formula (1) with another monomer that is copolymerisable with the acrylic monomer, or preferably with a vinyl monomer represented by general formula (2), that has an acid value of 5 mgKOH/g or less, is such that the viscosity of a 1% THF solution at a temperature of 25xc2x0 C. satisfies the specified range in a gelation test, does not gel in the manufacture of a heat resistant resin, and produces a heat resistant resin, with excellent transparency and mouldability, that can be moulded by melting. The acrylic polymer is readily lactone cyclised, and a heat resistant resin that boasts excellent thermoresistance among various features can be prepared from the acrylic polymer.
Further, an acrylic monomer composition containing a acrylic monomer represented by general formula (1) and another monomer that is copolymerisable with the acrylic monomer, as well as having an acid value of 5 mgKOH/g or less, is suitable as a material for an acrylic polymer having an acid value of 5 mgKOH/g or less. Therefore, the acrylic monomer composition can be suitably used as a material for an acrylic polymer having an acid value of 5 mgKOH/g or less, and also as a material for an acrylic polymer such that the viscosity of a 1% THF solution at a temperature of 25xc2x0 C. is in a range from 10 cps to 10,000 cps in a gelation test.
The heat resistant resin prepared in accordance with the present invention does not gel, boasts excellent transparency and mouldability, can be used in a wide variety of usage that requires thermoresistance.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.